This Research Project on Lung Maturation will focus on a number of functional and biochemical markers of lung maturation in animals provided to this project by the Preterm Lamb Core. These animals will have been treated by ultrasound injections as fetuses with hormones given as single doses and as combinations (corticosteroid, T3, TRH and EGF) to previously unmanipulated fetal sheep. The goals of this project are to characterize the pulmonary responses by evaluating postnatal lung function as assessed by sequential measurements of gas exchange, lung compliances, lung volumes (functional residual capacity and lung volumes at 40 cmH2O pressures) and responses to exogenous surfactant over the first five hours after preterm delivery. Subsequently, alveolar surfactant saturated phosphatidylcholine and SP-A pool sizes will be measured as will antioxidant enzyme levels and SP-A, SP-B, and SP-C in mRNA levels in lung tissue and type II cells isolated from the tissue. These multiple endpoints will reflect both functional and biochemical assessments of the induced lung maturation responses in preterm lambs exposed to short duration, clinically relevant hormone treatment strategies.